Orthogonal frequency-division multiplexing (OFDM) is a multi-carrier wireless communication technique that offers high spectral efficiency, robustness against multipath propagation and channel fading, and efficient frequency domain channel equalisation. However, there are some disadvantages associated with conventional OFDM transmission, such as high peak-to-average power ratio (PAPR), significant out-of-band emission (OOBE), and sensitivity to sampling frequency offset (SFO), carrier frequency offset (CFO), and phase noise.
A number of techniques have been proposed to overcome or mitigate the above-mentioned disadvantages and improve OFDM transmission performance. For example, to reduce PAPR, techniques of clipping, coding, phase optimization, nonlinear companding, tone reservation and tone injection, constellation shaping, partial transmission sequence and selective mapping, have been proposed. To reduce OOBE, notch filtering, guard band reserving, time-domain windowing, and cancellation using dedicated subcarriers have been proposed. However, the above-mentioned techniques are mostly used independently in conventional OFDM systems to tackle the respective disadvantages of conventional OFDM. Some of the techniques may in fact have conflicting effects. For example, the clipping method for reducing PAPR both introduces in-band distortion and increases OOBE. Notch filtering can reduce OOBE but it can also cause peak regrowth leading to higher PAPR. The effect of any given technique on the communication performance of OFDM as a whole is therefore somewhat equivocal at best.
There is therefore a need for a technique that is able to jointly mitigate at least two of the above mentioned disadvantages and thereby improve OFDM communication performance.